Multi-spindle machines are known in the prior art. Multi-spindle machines are used to mass produce standardized types of components. A multi-spindle machine typically has several work stations at which machining operations are performed. A piece of raw stock, such as a bar stock, enters the machine at a first station and as the machine indexes, various machining operations are performed. Once the station is indexed completely through the machine, a completed part is formed. The part is released, and the process is repeated for that station with a new piece of raw stock. An advantage of multi-spindle machines is that all stations in the machine are producing parts simultaneously, resulting in higher rates of production.
Multi-spindle machines (also referred to as multiple spindle machines) typically have a large indexing drum with four, five, six or eight stations thereon. Each of the stations carries a work piece. In all but one of the stations, where a new piece of stock enters, a machining operation is typically performed. After each machining operation is completed, the drum is rotated so that each work piece moves sequentially through the locations where the various machining operations are performed. Machining operations that are typically performed at a multi-spindle machine include milling, turning, and threading.
Most multi-spindle machines are very efficient in terms of producing standardized parts at a high rate. However, one drawback associated with a multi-spindle machine is that the entire machine operates off of a single main motor. The main motor simultaneously drives all of the devices and processes in the machine. Multi-spindle machines typically include a timing shaft with cams for the coordination of multiple machine operations.
There is always a risk that one of the mechanisms within the machine will not function properly. If such a malfunction should occur and not be detected by an operator in time to shut the machine off, the machine will continue with its next cycle. In such a case, an attempt by the machine to index to its next position could cause severe damage. This is why it is common for an operator to be required to closely monitor multi-spindle machines.
Typically, the speed of multi-spindle machines changes from high to low speed and back again during the course of the operating cycle. High speed is normally used for times in the machine cycle when critical machining operations are not occurring. High speed operation is desirable when the stations are indexing, or when the tools are moving toward or away from the work pieces and are not performing work thereon. Low speed operation is used when the tools in the machine are forming the metal. Any attempt to operate the machine at a high speed when such forming work is occurring is likely to cause a problem or jam the machine.
It is the responsibility of the operator or set-up technician to set the points in the machine cycle where the machine makes its high speed and low speed shifts. Shifting from high speed too early results in slower cycle times and production rates. Similarly, the same result occurs if the shift from low to high speed is made too late. However, as previously discussed, if the shift from high to low speed is made too late (or the shift from low to high speed too early) this can result in damage to the machine, the tooling, or the work piece.
A co-pending patent application titled Multi-Spindle Machine Retrofit System which is U.S. patent application Ser. No. 08/871,019 filed on Jun. 6, 1997, and its contents hereby incorporated by reference, describes a multi-spindle machine that uses a high and low speed system with a brake that decreases the cycle time, minimizes wear on the drive train gears, and enables a more effective operation of a multi-spindle machine. That multi-spindle machine retrofit system includes a control system for optimizing machine performance.
U.S. Pat. No. 5,730,037 filed on Apr. 17, 1995 and titled Multi-Spindle Machine Control System relates to a control system for optimizing multi-spindle machine performance. The patent describes use of a sensor in the proper positioning of stock that is fed into the multi-spindle machine. This patent and its contents are hereby incorporated by reference.
U.S. Pat. No. 5,676,031 filed on Apr. 17, 1995 and titled Apparatus For Detecting Stock relates to a multi-spindle machine. The patent describes a stock feeder arrangement having stock detection in a multi-spindle machine. This patent and its contents are hereby incorporated by reference.
U.S. Pat. No. 4,644,819 describes a high-low speed drive system for multiple spindle machines employing selective engagement and disengagement of associated pneumatic operated disc clutches.
U.S. Pat. No. 6,148,976 filed on Jun. 3, 1999 and titled Multi-Spindle Machine High Speed/Low Speed System, and its contents hereby incorporated by reference, describes a high and low speed system (also referred to as high/low speed) with a brake for a multi-spindle machine that decreases the cycle time, minimizes wear on the drive train gears, and enables a more effective operation of a multi-spindle machine. The high/low speed system includes the ability to selectively vary torque capacity to certain clutches with an adjustable pressure control. The system decreases the cycle time between high and low speeds.
With the prior art multi-spindle machines high speed operation is ongoing during feeding of new stock, such as a bar stock, into the machine. Generally multi-spindle machines include a stock stop device which acts to halt the advance of stock fed through a spindle by a stock feeder mechanism. These devices typically comprise a member, such as a plate or bolt, which may be fixed or otherwise accurately placed so that the stock is stopped at a desired distance from the forward edge of the spindle. These prior art devices often absorb the full impact of stock advancing during high speed machine operation. It has been discovered that because of the feeding of stock during high speed machine operation, the stock may hit the stop and bounce back from the stock stop device. This has sometimes led to the stock being held by the spindle collets in an inaccurate initial position. Hence, the stock is not properly positioned during machine operations. This may result in damage to tooling and the manufacture of defective parts.
Thus there exists a need for a multi-spindle machine having a high and low speed system that enables the feeding of stock at a lower speed during engagement of the stock and the stock stop device in order to provide more accurate positioning of the stock in the machine. Particularly, such a system would be preferably suited for retrofit on a Davenport Model B multi-spindle machine.